Clouds are a fascinating topic around here – especially since they are poised for a major makeover.
Most of the world has a rainy season. From California to Bombay, three months of the year deliver most of the annual rainfall. What makes our region fascinating is that we do have a cloudy season – but not a rainy season.
We receive 36 to 40 inches of rain annually. These are distributed quite evenly among the 12 months. You’d think that our cloud cover would be just as even. It isn’t. We enjoy a distinct period of mostly blue skies that envelops the summer and especially September and October – meaning right now. We’ve all noticed that this September was extraordinarily sunny. We experienced only a few cloudy days the entire month: a bit odd – but it would have been nearly unheard-of, had it happened in January.
That’s because a very interesting thing happens around November 1. Climate statistics show that our daily average cloud cover suddenly jumps from 35 percent to 65 percent virtually overnight. We go from mostly sunny to mainly overcast. This alteration is now just a couple of weeks away.
Another thing changes, cloudwise, for us. In summer, clear mornings with perhaps some early valley fog turn into afternoons with the sky peppered with individual puffy cumulus clouds. These are driven by convection: rising warm air created by the strong sun unevenly heating the ground. By late afternoon these puffballs dissipate, leaving the sky mostly clear again by sunset.
In September and October, when the sun is less strong, the cumulus tend to be less numerous and thinner, with much less vertical development. The thunderstorm potential thus plummets.
But watch what happens a couple of weeks from now when Mother Nature switches to her cold-weather mode. Quite suddenly in November – and lasting right through March – the weak sun and cold ground no longer produce upward-moving air. Individual puffy clouds become rarities. Thunderstorms are therefore scarce during our cold season. Instead, the cloud cover tends to be stratus or overcast. Visually, this is far less interesting to observe. We no longer see detailed, mutating cauliflowers overhead, but rather a single featureless gray sheet.
It’s odd that this striking annual pattern, parading overhead throughout our lives, tends to go unnoticed. However, since this dramatic increase in cloudiness and concomitant absence of sunshine happens at the same time that the very hours of daylight shrink to their yearly minimal, the gloom factor is psychologically inescapable. Coming as it does when the cold air chases away most of the birds, all the colorful flowers and all the deciduous leaves, the visual spectrum shrinks to muted hues and gray shades. Simultaneously, the crickets, peepers and the other zoological soundtracks go to “mute.” Our olfactory sense, too, becomes comatose in frigid air.
The outdoor environment becomes a sensory deprivation chamber. Only the tactile sense gets boosted, since winds are much stronger during the cold months; but few can honestly claim to enjoy the icy gusts. Some say that – despite all this – they love the winter. You have to salute these human outliers, since Seasonal Affective Disorder envelops 15 percent of the population.
For most of us, the solution is obvious: We must fill our leisure hours by going out to more restaurants. We must get fatter.
Want to learn more? To read Bob Berman’s previous “Night Sky” columns, visit our Almanac Weekly website at HudsonValleyAlmanacWeekly.com.